Next Generation COFDM
Microwave Links for
Military Surveillance
COFDM Delivers Combined Military
Surveillance and IP Data Links
COFDM: What Is It And Why Does It Work?
Surveillance Gathers Knowledge: Knowledge is Power
A Variety of Applications
Who Needs COFDM?

Sponsored by

Published by Global Business Media

Delivering world-class surveillance
and inhibition capability

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COFDM: What Is It And Why Does It Work? 8
Peter Dunwell, Correspondent

The Multipath Challenge
What is COFDM?
What it Means for Users
What COFDM Can Manage

Surveillance Gathers Knowledge:
Knowledge is Power

10

John Hancock, Editor

Surveillance is Not an Academic Matter
It Really is a Matter of Life and Death
New Technologies Delivering Established Principles
Some Things Have Changed…
… Others Remain the Same
Challenges to Surveillance
Coping with Anything

Enabling Technology
Other Uses
Police and Civil Applications
Military Service

References 16

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SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

Foreword
E

very now and then a technology comes

consider what the technology’s characteristics mean

along that can honestly be described as a

for users. We then look at the main purpose for which,

‘game-changer’. COFDM (Coded Orthogonal

in the context of this paper, COFDM is deployed –

Frequency Division Multiplexing) is such a

surveillance. What forces need to know may not have

technology. By quite simple but ingenious means,

changed much but the speed and accuracy with

it overcomes most of the hazards of wireless

which they need to know it has. Knowledge, as the

communication in difficult terrains, whether a city

article says, is power: so getting it and using it is critical

or mountainous landscape.

to success.

This Special Report opens with an article that looks

We then look at the variety of applications to

at Enterprise Control Systems Limited, an award

which COFDM had been put. In particular, we look

winning leader in the field of military surveillance,

at the disruptive effect that a technology that can

which supplies a number of key surveillance users with

communicate around corners and past mountains

advanced capabilities, taking advantage of COFDM

brings to the whole communication scene. And we

microwave links. COFDM is a spread spectrum radio

consider how the military are using the opportunities

transmission technique which splits the data stream

of COFDM. Last but not least, we ask ‘who needs

over multiple carriers with much slower symbol rate

COFDM?’ It’s great to have new toys in the box but

than a single carrier transmission. This gives resilience

we also need to know who can use them and for what

to multpath fading. The article goes on to describe

purpose. We look across a range of civilian, quasi-

EVENLODE, a lightweight data terminal specifically

military and military users of the technology.

designed to meet the demands of Unmanned Aerial

From the definition of its acronym to the technical

Vehicles (UAV), but which is equally well suited and

descriptions of how it works, this is never going to be

employed for other airborne, ground and maritime

a layman’s topic but we hope that our paper will allow

data applications. The article ends by describing

readers to understand a little more of what COFDM is

various operational advantages of the EVENLODE link.

and what it can do.

The report goes on to examine COFDM, what it is
and why does it work. It’s quite a technical section but
we’ve managed to find some layman’s explanations
to complement the technology rich ones. We also

John Hancock
Editor

John Hancock joined as Editor of Defence Reports in early 2012. A journalist for nearly 25
years, John has written and edited articles and papers on a range of defence, engineering
and technology topics as well as for key events in the sector. Subjects have included aeroengineering, testing, aviation IT, materials engineering, weapons research, supply chain,
logistics and naval engineering.

2 | www.defenceindustryreports.com

SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

ilitary Surveillance demands high
capacity, secure and robust data links
to deliver the multiple, high definition real time
images available from the sensors of modern
surveillance platforms. Range requirements
vary from tactical assets needing only 4-5
km through to long-range patrol surveillance
systems demanding capability at least to the
radio horizon.
Traditional VHF/UHF systems have provided
low data rates for voice and highly compressed
imagery. Satellite communications provide
Beyond Line of Sight (BLoS) capabilities, but
are severely capacity limited by virtue of both
their cost and availability. Traditional military and
commercial microwave Line of Sight (LoS) data
links can be infrastructure independent and have
been suitable for tactical ranges and for urban
surveillance if utilising suitable waveforms. A
typical application of standard microwave LoS
links has been to transmit surveillance video from
air platforms to the ground.
The latest COFDM data links used for
surveillance applications have now evolved

to include an IP link to the platform combined
with the high integrity, high capacity, military
grade security and extended range of the latest
generation of COFDM based systems. The
â&#x20AC;&#x2DC;uplinkâ&#x20AC;&#x2122; data path may be used to remote control
sensors and/or control unmanned systems
in the most demanding environments. As
surveillance sensors, their platforms and
capability have advanced they are now being
matched by the capability and flexibility of the
latest generation of COFDM microwave links that
combine, to best effect, many of the attributes of
legacy military data links with the performance
of the latest imagery transmission systems.
As surveillance sensor platforms become
smaller and more pervasive in the battle space,
COFDM microwave links are being adopted
by those needing to realise the true capability
of their sensors that are currently constrained
by legacy military communications systems.
Enterprise Control Systems (ECS), as an award
winning leader in this field, is already supplying a
number of key surveillance users with these
advanced capabilities.

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As surveillance
sensors, their platforms
and capability have
advanced they are now
being matched by the
capability and flexibility
of the latest generation of

ECS and COFDM
Coded Orthogonal Frequency Division
Multiplexing (COFDM) is a spread spectrum
radio transmission technique. COFDM splits
the data stream over multiple carriers with
much slower symbol rate than a single carrier
transmission. Using a much lower symbol rate
gives resilience to multipath fading. Additionally,
coding information is added to the data stream
and used at the receiver to estimate the most
likely transmitted signal state sequence. Each
subcarrier propagates slightly differently and
some subcarriers may be lost at a single receive
point. Using multiple subcarriers together with
diversity antennas provides an extremely robust
link far more resilient than a single carrier system.
The COFDM scheme is adopted as part of the
Digital Video Broadcast – Terrestrial (DVB-T)
standard and used to transmit Freeview in
the UK.

COFDM microwave links

Example of how COFDM copes with fading due
to multipath propagation

Enterprise Control Systems Ltd (ECS) has
since 2003 optimised the DVB-T standard for
surveillance use, tuning the implementation
to achieve the highest levels of integrity and
availability, security and range performance
that are essential to the military surveillance task.
This advanced ‘militarised’ implementation of
the already highly capable COFDM scheme
has been delivered to specialist customers
since 2004. The robust nature of this link, the
intuitive user interfaces provided and the aircraft

The EVENLODE Air Data Terminal

4 | www.defenceindustryreports.com

certification/type approval for all standard
systems are the reasons why over 200 airborne
ECS systems are now used for operationallycritical missions in over 40 countries. Continuing
advances in techniques and technology coupled
with the development of operational concepts
and battle space surveillance solutions have now
taken these capabilities to another level.

The ECS EVENLODE
Data Terminal
EVENLODE is the lightweight data terminal
specifically designed to meet the demands of
Unmanned Aerial Vehicles (UAV) but equally
well suited and employed for other airborne,
ground and maritime data applications. A pair
of EVENLODE data terminals behaves like an
Ethernet cable between networks at either end
of the link whilst simultaneously providing 2
High Definition (HD) video streams from the
sensor(s). With advanced, flexible and even
dynamic configuration control EVENLODE
provides an innovative solution for the most
demanding information exchange requirements
in surveillance systems.
The standard system provides 10 W Radio
Frequency (RF) output and has been proven to
provide links of up to 200 Nautical Miles (NM)
range and, up to 21 Mbps data exchange rate.
The system is available in L, S and C radio bands
and is DO160 approved for airborne installation.
The air equipment, at 3 kg for the standard
10 W system has been designed for UAV
and is modular. The standard EVENLODE air
data terminal comprises of Transceiver, Power
Regulation & Supply, Heat Exchange and, Linear
Power Amplifier modules. The modules may
be distributed for load balance, or be provided
to meet bespoke operational requirements.
A separate Video Encoder Module capable
of encoding up to two video signals and two
audio signals is supplied for direct video and
audio input. The Video Encoder Module has 4
High Definition (HD) and 2 Standard Definition

The EVENLODE Air Video Encoder Module

SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

(SD) inputs. Any video input may be selected
and switched, including during a mission, as
an input to the two video encoders with the
configuration and control of the Advanced Video
Codec (AVC/H.264/MPEG4 P10) compression
parameters also dynamically selectable. As
such the Video Encoder Module is offered as a
front-end video management system.
The data from the Air Video Encoder Module is

Example of how multipath propagation forms

presented to the transceiver as an Asynchronous
Serial Interface (ASI) (MPEG2 P1) along with
the Internet Protocol (IP) data and multiplexed
onto the Transport Stream. The Transport
Steam data is then modulated using a COFDM
technique and transmitted. An Internet Protocol
(IP) data buffer is incorporated as part of
the transceiver module to manage IP data
fluctuations that may momentarily exceed the
link capacity. So that data is not lost, IP data
is buffered at the transmitter section of the
transceiver and released as soon as the link
is capable of sending the buffer content. IP
communication is point-to-point. Critically, for
a surveillance asset, the ASI information (in
most cases the sensor output) is transmitted
omni-directionally to any number of receivers
within range, each of which decrypts the signal
to view it. In this way the EVENLODE system is
predominantly agnostic to the sensor platform
orientation or motion and provides a secure
data link from the platform to multiple receive
sites simultaneously, coupled with an IP link to
the platform to deliver any available IP based
functionality required.
To manage the trade-off between the available
data rate and the link range, an EVENLODE
system is provided with the ability to adjust the
radio link parameters and optimise them for the
surveillance task. The way in which this control
is implemented is bespoke to customer, sensor
and platform requirements. This control may be
based on the assessment of the link range with
Global Positioning System (GPS) data sent
between the two link data terminals, by user
control, by automatic sensing of the required
data rate for the information requested to be sent
or, by automatic link monitoring between the two
data terminals.
EVENLODE ground data terminals may be
provided specific to operational requirements
with options for mobile, portable and static

systems. A majority network voting system
may be used to link any number of ground data
terminals onto an IP area network backbone. The
Network Voting System automatically selects the
best receive signal available in the network and
uses this to multicast received ASI data securely
to any number of monitoring sites. Uplinks from
a network voting system are achieved by DVB-T
Single Frequency Network (SFN) techniques
and transmitting the same signal from every
ground data terminal or, selectively by knowledge
of the position of the platform.
The EVENLODE System is extremely flexible
and can be configured to meet the demands
of highly capable surveillance sensor systems.
With close human factors analysis of customersâ&#x20AC;&#x2122;
requirements, Enterprise Control Systems Ltd
(ECS) is able to provide intuitive interfaces to
EVENLODE systems and provide pre-set profiles
for specific operational tasks, or even tighter
integration into mission systems.
Fully embedded security is always provided,
carefully integrated into these advanced systems
so as to work in seamlessly with the complex
demands of full motion video communication.
Systems are supplied with either integrated
Advanced Encryption Standard (AES)
256-bit (subject to export license) or Substitution
Cipher encryption.

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Benefits of the Next Generation
of COFDM Systems
Internet Protocol (IP) is fast becoming a
ubiquitous interconnection standard within all
platforms from the individual soldier system,
through specialist battlefield vehicles, to
ships, to aircraft and unmanned systems.
For example Avionics Full Duplex Switched
Ethernet (AFDX / ARINC 664 Part 7) is a
standard that is replacing bus systems such
as ARINC 429 for data exchange requirements
on air platforms. It is therefore essential to
integrate with these IP data bus systems.
Extending the platform IP data bus with an IP
communications link that is already embedded
within the encrypted COFDM data link from
the sensor platform delivers a significant
capability gain. The user gets a smaller, lighter,
more efficient and substantially less complex
system. These performance and capability
improvements coupled with reduced size, weight
and power consumption are most apparent on
the surveillance platform itself, with a lower
box/equipment count. However, the system
improvement continues to roll out through
the receive networks across the large number
of potential consumers of the surveillance
product, all of whom benefit from the simplicity,
the tighter system integration and the increased
performance available.

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The EVENLODE System
is extremely flexible and
can be configured to
meet the demands
Example of a MPEG 2 multiplexer and COFDM modulator transmit chain

of today’s highly
capable surveillance
sensor systems.

The leading manufacturers of platform Electro
Optical (EO) camera turrets continue with the
Standard Digital Interface video outputs as their
output of choice. These SDI outputs can be
encoded and indexed on an MPEG2 P1 Transport
Stream and sent as a Constant Bit Rate (CBR)
datalink payload. The Transport Stream may be
encapsulated with IP and presented onto an IP
network using one-directional protocols such
as Unidirectional Datagram Protocol (UDP) or,
the SDI may be encoded and presented to the
IP network without indexing on a Transport
Stream using Real Time Protocol (RTP) and a
jitter buffer at the receiver. Control of platform
sensors is increasingly IP-based. Therefore
systems such as EVENLODE provide the ability
to control platform sensors remotely over the
COFDM link with the ability to send both SDI
video via the Video Encoder Module, or any IP
based information.
EVENLODE provides a remote IP network
link which gives all manner of operational
advantages. The EVENLODE link may be used
to provide a remote terminal access on the sensor
platform into a database or server system. The
platform then has access to the server system
information such as mapping, operational
tasking and intelligence with remote access into
this information over the COFDM EVENLODE link.
In this way, the storage of sensitive information
on the sensor platform is minimized and can be
denied should the platform be compromised. The
IP link may be used for messaging, transferring
files, Video over IP and, to provide ’interneton-the-platform’. As an example, in the case
of manned air surveillance platforms, it is now
feasible to relocate the air surveillance sensor
operator from the platform, to the controlling, or
sensor data consuming node.
COFDM transmission, as a spread spectrum
technique using multiple carriers, occupies a

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significant bandwidth. It is therefore absolutely
essential to derive maximum operational benefit
from this critical battlefield resource. Payload data
rate is proportional to the bandwidth allocated in
the available spectrum. Data links are therefore
available for frequency ranges between 1 and
6.5 GHz (L, S and C Band). Users are also
under pressure to release frequency spectrum
to facilitate commercial mobile data services.
So, bandwidth is a premium. EVENLODE uses
Advanced Video Coded (AVC/H.264/MPEG4
P10) to code sensor video with significant
improvements in compression for the same
quality image over older legacy encoding
techniques such as MPEG 2 P2/H.262. This
means that the same quality full motion image
may be sent via an EVENLODE link using
less bandwidth with the added advantage that
lower bandwidth signals are also capable of
greater ranges (Thermal noise is proportional
to bandwidth). Incorporating variable
bandwidth setting and the AVC codec, allows
EVENLODE to provide the optimum link range
performance for any data exchange requirement.
Enabling expert user control of these parameters
in a dynamic manner, even during a mission,
enables the user to actively ‘fight’ the system
in the RF/cyber/ISTAR domain to maintain
operational effectiveness and combat attempts
by an opponent to deny it.
The highly optimized ECS COFDM radio
spread spectrum technique has been proven
on operations in Line of Sight (LoS) and
Near-Line of Sight (NLOS) environments, in
high multipath environments in the land, maritime
and air domains and on air platforms ranging
from rotary to fast jets. As waveforms and
techniques continue to evolve and standards
to emerge, the latest generation EVENLODE
system has been designed with interoperability
in mind. Utilizing the soft-core boards,

SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

As the surveillance ‘eyes’ of the battle space play
an increasingly critical role in the execution of
operations, it makes sense that everyone across
multiple domains is able to exploit to

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best effect what these ‘eyes’ can see

waveforms may effectively be programmed and
‘ported’ onto the soft cores so that EVENLODE
may be configured with other waveforms for
interoperability. Flexibility, configurability and
longevity of use in a demanding and changing
battle space will always remain another key
aspect to the selection and deployment of
mission critical capability.
As the surveillance ‘eyes’ of the battle
space play an increasingly critical role in the
execution of operations, it makes sense that
everyone across multiple domains is able to
exploit to best effect what these ‘eyes’ can see.
Today’s sensor platforms are increasingly
becoming ‘un-tethered’ from their single points
of control and single points of product ingest
into the battle space. The dissemination of
surveillance product direct from the sensor
platform to the widest number of potential
users, without adding the burden of complex
user to user transport has been happening as
a quiet revolution for some time. The continued
deployment of advanced, COFDM techniques
optimized for the military surveillance domain
and their combination with platform and
networked C2 is adding yet another stepchange improvement in the delivery of this
vital commodity.

SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

COFDM: What Is It
And Why Does It Work?
Peter Dunwell, Correspondent

COFDM is a modulation
scheme that divides
a single digital signal
across 1,000 or
more signal carriers
simultaneously. The
signals are sent at right
angles to each other
(hence, orthogonal)
so they do not interfere
with each other

W

e live in a world where, even for the
armed forces charged to protect us,
cost constraints have to be considered. Thus,
if a product or system can offer improved
performance without significant additional
cost, it is likely to prove popular. COFDM is one
such system but, that said, it’s not the easiest
concept to describe. Rather like the system
itself, it might be best approached along a
number of paths, some quite technical, others
a little more accessible.

The Multipath Challenge
The challenge that COFDM has to overcome
is called multipath. “Multipath,” according to
Scribd1, “is the term for the different paths that
a signal takes in reaching an aerial from the
transmitter. For example, one path may be a
line-of-sight path from the transmitter to the
aerial whereas another path may bounce off a
hill or building before reaching the aerial. In this
example, the signal that travels along the lineof-sight path arrives at the aerial first followed a
short period later by the path that has bounced off
the hill or building. As the different paths travelled
are of different length the time taken for the signal
to reach the receiver will be different, with the
direct path (if there is one) reaching the receiver
first, followed by reflected paths. The effect that
these multipaths have on the received signal at
the antenna is that the amplitude of the received
signal fluctuates.

What is COFDM?
COFDM is the anagram for Coded Orthogonal
Frequency Division Multiplexing. JH Stott of
BBC Research and Development makes the
technical case2; “COFDM can cope with high
levels of multipath propagation, with a wide
spread of delays between the received signals.
This leads to the concept of single-frequency
networks in which many transmitters send
the same signal on the same frequency,
generating “artificial multipath”. COFDM
also copes well with co-channel narrowband
interference, as may be caused by the carriers
of existing analogue services.”
8 | www.defenceindustryreports.com

COFDM sends its message using multiple
transmitters all on the same frequency (frequency
division multiplexing) which are transmitted at
right angles to each other. This has the effect of
enabling the signal to cope with terrain related
disruption better than if only one transmitter is
used and the whole signal goes in the same
direction, and that makes it very good for
surveillance systems.
This is quite a technical area so that, inevitably,
explanations tend towards the technical; such
as Tektronix3, “’Coded’ means that the data to
be modulated has error control. ‘Orthogonality’
means that the spectra of the individual
carriers do not influence each other... A singlefrequency network is used for the actual
transmission. This is a modulation scheme
used for digital transmission that is employed by
the European DVB system. It uses a very large
number of carriers (hundreds or thousands), each
carrying data at a very low rate... It is, therefore,
particularly suited for mobile reception and for
single-frequency networks.”

What it Means for Users
Perhaps a less technical but more accessible
explanation comes from TechTarget on
SearchNetworking4; “COFDM is a modulation
scheme that divides a single digital signal across
1,000 or more signal carriers simultaneously. The
signals are sent at right angles to each other
(hence, orthogonal) so they do not interfere with
each other.” The articles can also be mined to
find a refreshingly straightforward description
of ‘modulation’ as, “the addition of information
(or the signal) to an electronic or optical signal
carrier... One can think of blanket waving as a form
of modulation used in smoke signal transmission
(the carrier being a steady stream of smoke).”
Armed Forces International also explains the
problem in slightly more accessible terms and
relates it to surveillance operations5; “Covert and
surveillance operations are unconventional by
design. So, the normal lines of communication
may be rendered ineffective, which translates into
the need for UGVs [unmanned ground vehicles]
to operate in non-traditional environments,

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Delivering world-class
surveillance and
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32mm self contained Electromagnetic Compatibility Chamber

specifically non-line-of-sight environments.
When necessary, microwave links must provide
encrypted, COFDM real-time, high-quality
video to all interested parties… traditional
video microwave requires line-of-sight from the
transmitter to the receiver, even slight obstructions
can cause multipath or ghosting effects. At the
very least, the signal is distorted or fades out.
At the very worst, the signal is lost altogether.”

What COFDM Can Manage
What may be of more interest to users is that
COFDM enables signals to cope with terrain
and infrastructure that might have blocked older
transmission systems because its multiplicity
of transmitters and variability of direction
mean that, where there is an obstruction,
different transmissions will ‘approach’ it at
different angles ensuring that some will get
past. It has been described as allowing signals
to ‘flow’ around obstructions.
Interestingly, OFDM/COFDM has seen a lot of
development in connection with digital television
and audio broadcasting. The reasons for this
are that, being less vulnerable to disruption, it is
better able to maintain the quality and integrity
of terrestrial high definition television (HDTV)
and digital audio broadcasting (DAB) where
it not only copes with terrain and environment
related disruption but also can deal with
changes experienced by a moving receiver, such
as in a car. COFDM has made DAB car radio

COFDM enables signals
Identify early Decide fast

to cope with terrain and
infrastructure that might
have blocked older
transmission systems

possible. While this has no particular surveillance
relevance, it illustrates the capabilities of OFDM/
COFDM links.
The concept actually grew out of Multi Carrier
Modulation (MCM) developed for military high
frequency (HF) radios in the late 1950s which
divided streams [messages] into several parallel
streams used to modulate several carriers6. And
it is still military applications where a lot of the
progress is being made with the development of
COFDM mesh7 to improve surveillance prospects
by combining a number of COFDM radios
together over a wide area so that whichever one
is able to get the best surveillance, the whole
mesh can be used.

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Surveillance Gathers
Knowledge: Knowledge
is Power
John Hancock, Editor

It has always been a vital part of military activity to know as much as
possible about the enemy and to communicate that knowledge to planners

The armed services
might regard the quality
of surveillance in
terms of the difference
between knowing the
enemy’s plans, positions
and routes or being
caught out by a surprise
assault… the difference
between life and death

Surveillance is Not
an Academic Matter
Surveillance; it excites opinions at polar opposite
ends of the spectrum of human reactions. Some
see modern surveillance systems as intrusive
agents of the ‘Nanny State’; others see them as
legitimate technology to deter offenders (where
they are overt) or catch transgressors (when they
may be less than overt). But while those of us
living in the comparably comfortable realms of a
civil society may argue over this, there are others
for whom surveillance is not simply a convenient
way to deter or spot transgressors who might be
jumping the traffic lights or using a mobile phone
whilst driving.

It Really is a Matter
of Life and Death
Members of the armed services might regard
the quality of surveillance in terms of the
difference between knowing the enemy’s plans,
positions and routes or being caught out by a
surprise assault… the difference between life
and death. For the military (army, navy or air
force) surveillance to gather intelligence has long
been the prerequisite to success in battle. Of
course the calibre of the people and the quality
of the equipment with which they fight are massive
factors but, as guerrillas from the Vietcong to the
Taliban insurgents in Afghanistan have shown,
knowing the terrain on which you are fighting,
knowing your enemy’s dispositions and strength,
and being able to deny the enemy that knowledge
of your forces can enable militarily weaker fighters
to inflict steady and degrading damage to a larger,
better equipped force.

New Technologies Delivering
Established Principles
These days, the range of questions for which
surveillance is the answer is larger than ever but
10 | www.defenceindustryreports.com

essentially it is the same technique as has been
applied for thousands of years. The technology
might have evolved and the methods might
have been adapted to cope with new
threats and new ways of war fighting but the
essentials remain the same. The first need is
to know what is happening in the area around
your position from where any attack could
be mounted. At one time, that was one
reason why fortresses and castles were built
on the highest ground possible: not only
was it possible to physically dominate the
area around and easier to defend against
attackers who had to climb up to reach you
but, the higher your vantage point the better
you could see them coming and ‘read’ their
tactics. Today, attacks can come from a far wider
area than what can be seen from your positions
and so we put surveillance aircraft into the sky
and even satellites to enable us to see what our
enemies and potential enemies are doing. But
for all their sophistication, they still have to get
the fruits of their surveillance back to the people
running the battle.

Some Things Have Changed…
The need has changed in other ways as well. The
asymmetric type of war that armed forces more
often have to fight today is against an enemy who
is less predictable, less likely to be organised in
obvious formations and more likely to look like the
general population than like a fighter. Therefore
not only do surveillance techniques have to be
different but also the speed and quality of the
transmission of data that has been gathered to a
place or (more likely) a processor that can discern
a pattern and predict what is likely to happen have
become critical.
A more worrying scenario is when that
undistinguishable fighter comes into one of our
cities with an explosive device or worse. Not only

SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

Battlefield protection and troop protection remain key
priorities in any action and it will usually be surveillance
Delivering world-class
surveillance and
inhibition capability

that will enable troops on the ground to call in and
provide targets for support forces and/or air strikes

do we need surveillance to tell us from where
the threats might be coming but we also need
to be able locate, identify and track any of the
modern weapons that might be used against
us such as chemical and germ weapons or
even nuclear devices. The world is no longer a
predictable place so the people with the most up
to date, accurate and comprehensive knowledge
will have the upper hand.
We also face a low level but general threat of
attack from across the world using Intercontinental
Ballistic Missiles and, again, the only way to
counter this is with knowledge gained through
surveillance. Without that, the anti-missile missiles
would not know where to go. And, given the speed
of such weapons, the value of any surveillance will
be significantly enhanced by rapid and reliable
transmission of the knowledge learned to a device
that can use it.

… Others Remain the Same
But, not everything in warfare has changed so
much. One of the critical tasks of surveillance, even
in the modern war, is to discover and understand
the enemy’s positions and, from any discernible
deployments, his plans. Scouts used to have to get
themselves near to the enemy positions in order to
survey them and to eavesdrop on discussions in
order to learn plans. Today, that can often be done
from an aircraft or even a ground station such as
GCHQ using telephone taps or eavesdropping on
various wireless communications. However, we
keep returning to the fact that a station such as
GCHQ is only as good as the quality of information
it receives and in a fast moving world that is often
only as good as the speed and quality with which
it is transmitted from source to processor.
And while wars might be increasingly asymmetric
with enemy combatants not easily distinguished
from the rest of the population and almost no setpiece battles, there are still significant fire fights

in which soldiers still lose their lives. Battlefield
protection and troop protection remain key
priorities in any action and it will usually be
surveillance that will enable troops on the ground
to call in and provide targets for support forces
and/or air strikes.
Another fact of any military campaign is that a
force needs supplies. That can be tricky when the
routes from rear supply bases to operational and
front line bases have to run through potentially
hostile territory. Convoys are often accompanied
by UAVs (unmanned aerial vehicles) whose task is
to constantly survey the terrain around and along
the convoy’s route.

Identify early Decide fast

Challenges to Surveillance
As much as combatants endeavour to gather
knowledge about the other side, other forces will
endeavour to detect and/or disrupt their efforts
with a range of counter measures. And, when
the campaign is conducted in difficult terrain,
the terrain itself or even weather conditions will
have the capacity to disrupt communications.
Forces need to take measures to ensure that
all surveillance data is quickly and accurately
transmitted to a processor wherever they are,
whether in a mountainous area or an urban area
where building can disrupt.

Coping with Anything
Knowledge and communication have always
been key elements for military campaigns.
However, today’s battlefield information
needs to be gathered over a much wider area
in a range of formats to support not only human
decision-making but also technology-based
analysis and prediction. And any intelligence
gathering system today must be able to
cope with difficult terrain, hills, valleys, buildings
and trees, any one of which could disrupt sighting
or communication.

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SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

A Variety of Applications
Francis Slade, Staff Writer

COFDM is making its mark in both the civil and military worlds
but for very similar and transferable purposes

These days and to an
increasing degree,
governments and
public authorities use
surveillance as one tool
in their efforts to maintain
safe streets and manage
the areas for which they
are responsible

Convergence and Disruption
Create a New Paradigm
Two of the most potent terms in technology today
are ‘convergence’ and ‘disruption’. Convergence
is easy enough to explain; it’s where two or more
technologies come together to create a device
with multiple capabilities such as mobile phones
with web capability, music players and cameras.
Disruption almost suggests a negative effect
whereas it really means the creation of a new
paradigm, such as the same mobile phone’s
impact on the retail music market and the rise of
people’s journalism.
These effects can also be founds in the realms
of communication links where the technology of
COFDM is, as its acronymic nature results from
the convergence of several other technologies
(explained elsewhere in this paper). It has also
made possible a number of applications that
might previously have been problematic. Some
of these are in the civil realm and, while this is
a defence inclined paper, there is sometimes
something to be learned from civilian applications
of shared technologies.
At the 20th International Television Symposium
in 1997, JH Stott of the BBC explained8; “Coded
Orthogonal Frequency Division Multiplexing
(COFDM) has been specified for Digital
Broadcasting systems for both audio – Digital
Audio Broadcasting (DAB) – and (terrestrial)
television – Digital Video Broadcasting (DVB-T).
COFDM is particularly well matched to
these applications, since it is very tolerant of
the effects of multipath (provided a suitable
guard interval is used)… However, rather more
is involved than simply adding coding -- the ‘C’
-- to an uncoded OFDM system. The coding and
decoding is integrated in a way which is specially
tailored to frequency-dependent channels and
brings much better performance than might
be thought based on a casual inspection.”
It is COFDM’s ability to cope with the
potentially disruptive effects of urban structures
that makes it particularly suitable for terrestrial
digital broadcasting.

12 | www.defenceindustryreports.com

Capability Transfer
This ubiquity of capability can then be transferred
to a more militaristic purpose, surveillance. These
days and to an increasing degree, governments
and public authorities use surveillance as one
tool in their efforts to maintain safe streets
and manage the areas for which they are
responsible. But, in an urban environment,
surveillance, like any broadcast system, can
be subject to disruption from the effects of
the Urban infrastructure. COFDM can be
applicable here. “An entire city can be covered
by COFDM video and IP solutions, enabling
government and law enforcement authorities
to protect citizens, keep transport infrastructure
running smoothly and combat major crime,
terrorism and drug trafficking. With high
powered receivers mounted at strategic elevated
positions, video and audio information can be
transmitted to local and central monitoring
points… [And] If first responders, such as the
ambulance service, utilise body worn cameras
at the scene of an accident, they can send
pictures via strategically placed receivers direct
to the nearest hospital, enabling accident and
emergency personnel to prepare for incoming
patients. Once mobile in the ambulance, all
the patient’s vital signs can be shared with the
doctors and they can, in turn, offer additional
advice to paramedics if needed.”9

Technology Transfer
It doesn’t take a great leap of imagination to see
how this use type of application for COFDM can
translate into a useful additional tool for military
surveillance operations. It can deal with difficult
terrain and levels of interference to transmit a true
signal from the point of intelligence gathering to
the point of analysis, decision and action initiation.
Mission outcomes in military surveillance terms
are often dependent on the capability of the whole
system to exchange information with maximum
speed and integrity so that not only can the
specific information be acted on expeditiously
but also in light of the wider situational awareness.

SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

Delivering world-class
surveillance and
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Lynx Helicopter

But, of course, as much as a military force
wishes to preserve the quality of surveillance and
information, an enemy, especially a technically
advanced enemy, will wish to disrupt both the
gathering and communication of data. To that
end, the British Army has developed a number
of digital communications systems to function
in, “An extremely complex environment where
increasingly large amounts of information must
flow without interruption, whilst being protected
from exploitation or disruption by a technically
advanced enemy.”10

Land, Sea and Air
This issue has become even more pertinent
with the advent of unmanned ground vehicles
(UGVs) in the surveillance role. As Armed Forces
International puts it11; “while the shape & size
of these unmanned vehicles will continue to
evolve, one requirement will remain constant the communications link between personnel and
UGVs must be as reliable as the information being
gathered. Video, audio, data must be brought
back in real-time, clearly, and flawlessly. With
robust communications equipment essential
to transmitting high bandwidth traffic over
terrestrial or satellite networks, high quality digital
microwave and COFDM technology provide the
ideal solution.”

The PA Consultancy Group’s report, Defence
Demand for Spectrum 2008-2027 acknowledged
the part that COFDM could contribute for the MoD
in getting the best return for the communications
spectrum available to it12.
Given the range of tasks to which armed
forces are now applied, surveillance does not
always occur in battle conditions but might as
likely occur at sea where forces are deployed to
deal with piracy or drug smuggling. As on land,
a COFDM digital video transmitter with integral
cameras and GPS will provide a vital and secure
situational awareness system for sea based law
enforcement operations. The same will also apply
for air to ground communication requirements
where aircraft (often unmanned) are used for
theatre surveillance or to track individual threats.
The information will need to be sent to the
operational bases very quickly and accurately to
allow a proper course of action to be determined.

Identify early Decide fast

Disruptive Technology
COFDM does not only enhance the quality and
speed of communications, it makes possible
new types of warfare such as we are increasingly
seeing in areas where nobody wishes to risk
‘boots on the ground’ but where intelligence and
action are necessary – truly disruptive technology
in every sense.
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SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

Who Needs COFDM?
Peter Dunwell, Correspondent

It’s surprising how many great applications there are
for a technology that revolutionises communications links

The system copes well
when line of sight is
not always available
because the way it
constructs transmissions
allows signals to go
around obstacles without
causing interference at
the receiving end

Enabling Technology
COFDM is the enabling technology behind
a revolution in broadcasting and electronic
communications. In his paper, ‘The how and
why of COFDM’, JH Stott explains; “DAB
(unlike its AM and FM predecessors) was
especially designed to cope with the rigours
of reception in moving cars – especially the
problem of multipath reception which, in this
case, is time-varying. For DVB-T, a higher capacity
than DAB was essential, mobile reception was
not a priority, but multi-path tolerance was still
important because of the widespread use of
set-top TV antennas. A new form of modulation
– COFDM – was chosen for both systems, albeit
with differences in detail, and with appropriate
changes of parameters, to suit the different
requirements of DAB and DVB-T. Both systems
include a degree of flexibility.”

Other Uses
That ‘all-terrain’ ability to function without line
of sight is also useful in other contexts. News
organisations that need to be able to survey
a cityscape for local programming find that
COFDM allows them far more scope in where
they go and from where they can broadcast.
COFDM offers a number of advantages over
conventional microwave for which either a line
of sight or a devised path is necessary in order
to get food communication. Also conventional
microwaves can be distorted. COFDM
does not require line of sight or a devised
pathway nor will it be degraded or distorted by
outside influences.
The system copes well when line of sight
is not always available because the way it
constructs transmissions allows signals to go
around obstacles without causing interference
at the receiving end (see elsewhere in this
paper for technical explanations). Microwave
Communications14 described the capability as,
“[benefitting] greatly from the inherent multipath

14 | www.defenceindustryreports.com

advantages that COFDM provides; if a few
carriers are lost to multipath, the lost data can
be easily recovered by error coding.” COFDM
can cope better than other systems with echoes
and reflections.

Police and Civil Applications
Police forces certainly understand the value.
For instance, for the Beijing Olympics, Beijing
Police used two helicopters, vehicles and a base
network fitted with COFDM technology from a
British firm to enhance their ability to manage
the Olympic park, its environs and the wider
city during the event. The equipment enabled
the police to upload pictures from vehicles so
that the picture could then be re-broadcast
simultaneously along with an image from
the gyro stabilised camera mounted on the
helicopter. This ability to achieve real-time
surveillance data use gave the police instant
situational awareness which was described as
a force multiplier, i.e. it allowed the police to do
more and to do it more effectively.
In other applications, COFDM is a valued part
of the ‘protection’ toolkit for those assigned to
protect VIPs15. “The mobility of the VIPs determines
the technology that has been employed as
well as its flexibility and portability. The mobility
of the operations as well as the targets needs
to be covered with appropriate surveillance
systems. Surveillance requires that information
be consolidated, stored and ultimately processed
[in] real time in order for the management to be
able to control on the spot decisions inside the
headquarters. The systems should be such that
there is no gap between the on-site operation
and the centralised information management…
With increased insecurities among the royalties,
celebrities and various government dignitaries,
there is a high demand for RF jamming
capabilities from the security personnel. The UK
came up with the first digital COFDM Microwave
links late in the 1990s for video surveillance.

SPECIAL REPORT: NEXT GENERATION COFDM MICROWAVE LINKS FOR MILITARY SURVEILLANCE

The UK came up with the first digital COFDM
Microwave links late in the 1990s for video surveillance.
These should be provided alongside military
Delivering world-class
surveillance and
inhibition capability

surveillance as well as police control systems

Closely spaced sub-carrier of a COFDM signal

These should be provided alongside military
surveillance as well as police control systems.
In video surveillance systems, there should be
safe and secure COFDM Microwave uplinks and
downlinks to the international helicopter providers
for a complete VIP protection. Covert and overt
COFDM video surveillance systems enable the
security personnel to monitor and record critical
data through line of sight (LOS) and non-line of
sight (NLOS) transmission systems. They are
used in infrastructure protection, monitoring
serious crimes, policing public order as well as
identifying and monitoring terrorist threats.”
As well as police and protection forces, border
guards find the system greatly improves their
performance. “The Estonian Police and Border
Guard have recently received delivery of a state
of the art COFDM Microwave Downlink System
designed and manufactured by [a British
supplier] to equip their new AW139 medium
twin helicopters. The downlink equipment will

be crucial in air surveillance, search and rescue
services, government missions, border patrol,
medical missions and general utility duties to
support the community.”16
It is also a useful technology for communication
in previously ‘hostile to communication’ places
such as mines using a mesh in which one of the
mesh nodes is run along the main mine shaft to
facilitate Ethernet, data, video and audio services.
It doesn’t just offer mine security but also can add
to mine safety with better communications and
the ability to monitor machinery.

Identify early Decide fast

Military Service
In military service17, “COFDM digital microwave
provides clear advantages over alternative
radio technologies in the delivery of video,
audio, and data. These advantages are easily
demonstrated over long distances and in
unforgiving environments where significant
multipath interference occurs.”
COFDM based technologies can support
specific operations such as the sea and air
surveillance of a particular area. They can
also focus down to one battlefield where an
individual unit can detect threats and where they
are coming from in order to inform their own
actions or to call in external force such as air
strikes. And a whole surveillance system to serve
national security and defence can use COFDM
technology in linking units on land, at sea and
in the air with the main command centre and
mission management centre.

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